This invention relates to an electroless nickel plating method and apparatus, and more particularly to a method and an apparatus for the electroless nickel plating of long bodies.
Although electroless nickel plating of bodies of all types is known, nevertheless bodies of exceptional length, such as pipes, tubes or pump bodies are difficult to plate uniformly.
Conveniently, long bodies or articles, such as tubes and pipes, are supported horizontally within an elongated plating tank. The electroless nickel plating solution is heated, and sometimes agitated, to plate the horizontal body immersed within the solution in the tank. Foreign particles in the bath or solution tend to gravitate down upon the upper exposed surfaces of the body. Such foreign particles deposited upon the upper surfaces tend to plate upon the surfaces by virtue of an auto-catalytic reduction reaction. Thus, the particulate matter co-deposits with the plating material, so that the overall coating of the object is non-uniform.
Hydrogen bubbles, which are by-products of the electroless solution reaction, have a tendency to rise and adhere to lower exposed surfaces. Where the hydrogen bubbles adhere to the surface, there is little, if any, plating action by the electroless nickel solution. Accordingly, such areas are thinly plated.
Similar, but accentuated, deposits of particulate matter and voids from hydrogen bubbles occur on the interior surfaces of bodies, such as the interior opening of a long pipe, through which circulation of the solution is difficult, particularly at the same flow rate as the solution on the exterior surfaces of the bodies. The longer the bodies, the more non-uniform the plating is apt to be.
Furthermore, exceptionally long bodies present space problems, as well as additional manufacturing costs in producing very long horizontal plating tanks.
Where there is considerable weight in the long body to be plated, more supports must be provided in order to prevent the long body from bending or bowing. Where additional supports or brackets are provided for mounting the long body within the tank to maintain the longitudinal axis of the body in a substantially straight line, then those areas of the body engaging the supports will not be plated.